I got a question today from someone submitting a research protocol to the Institutional Review Board (IRB). The IRB had some concerns about the power calculation. In particular, they said “The IRB would like to know, how you set the parameters for the power calculation, such as effect size, alpha level. For effect size, you need to have some data to justify or should choose a conservative one.”

Part of this was due to an error in the submission of the protocol. We had specified a paired t-test rather than an independent samples t-test, which is a major gaffe on my part. But they were pushing into some tricky territory and I wanted to clear things up. Here is the response that I suggested that we share with the IRB. Continue reading →

I was working with a client who had a limited population of medical residents to choose from, and it would be a struggle to get even 60 of them. The primary outcome was binary: whether a certain medical procedure was run properly in a test setting. The intervention was special training on a model; the control was normal training without the model. I got a phone call back that said, what would the power be if I used three groups rather than two?  I thought to myself “Good grief!” You can’t say that to a client, of course, so here’s what I said. Continue reading →